Electronic structure of RuSr2EuCu2O8studied by x-ray absorption and photoemission spectroscopies

Abstract

Local electronic structures of ruthenocuprate RuSr${}_{2}$EuCu${}_{2}$O${}_{8}$ (RuEu-1212) were investigated by using x-ray absorption near-edge structure (XANES) and valence-band photoemission (VB-PES) measurements at room temperature, 80 K, and 25 K. The XANES results indicate that when RuEu-1212 is below Curie temperature, ${T}_{\mathrm{M}}$, electrons are transferred not only from Cu 3$d$ states, but also from Ru 4$\phantom{\rule{0.16em}{0ex}}d$ states, to O 2$p$ orbitals. Additionally, the partial spectral weight distributions derived from VB-PES measurements provide evidence of a weak overlapping between Ru 4$\phantom{\rule{0.16em}{0ex}}d$ states and strongly Cu 3$d\ensuremath{-}$O 2$p$ hybridized states below the Fermi level, which results in a weak coupling between the CuO${}_{2}$ and RuO${}_{2}$ layers. The analysis of extended x-ray absorption fine structure shows that the appearance of weak ferromagnetism and superconductivity is accompanied by a significant decrease of dynamic local lattice distortions of high-shell Cu-Sr and Ru-Sr bonding in RuEu-1212.